That is false. Safety engineering sometimes only mitigates risk, but often reduces it to practically zero, such that people have to be deliberately negligent to prevail in bringing about a safety incident. E.g. elevator holds 15 people, yet 45 somehow jam themselves in as a stunt.
Partial safety mitigation isn't so much how safety engineering works; it's how it ducks out of working due to non-engineering reasons. If any safety issue remains, that means engineering was not done in that regard: the safety engineers were excused from the requirement to design anything for that risk.
That's just simply not how safety engineering works. Safety features mitigate risk, none of them solve it.